1. Field of the Invention
The present invention relates to a linear motion guide unit in which a sliding element movable on a rail track in a linearly sliding manner is provided therein with lubricating plate assemblies.
2. Description of the Prior Art
The recently remarkable development in mechatronics technology increasingly requires linear motion guide units improved in precision, speed and miniature and the use of such apparatus extends into many technical fields. The linear motion guide units are extensively incorporated in reciprocating apparatus, which is in general employed in semiconductor manufacturing apparatus, inspection instruments, industrial robots and the like. The linear motion guide units recently become required to meet with needs of maintenance-free as well as high precision, high speed and miniature. To cope with the needs, the linear motion guide unit has required the self lubrication of long service life on its relatively movable sliding areas.
A conventional linear motion guide unit, as shown in FIG. 20, has a track rail 2 and a sliding element, or slider 1, saddling the track rail 2. The track rail 2 is formed on lengthwise side surfaces 3 thereof with raceway grooves 4 and the slider 1 may move on the track rail 2 by virtue of rolling elements 7 running through the raceway groove 4. The track rail 1 has on lengthwise upper surface 14 thereof openings 13 spaced from each other. The track rail 2 is fixed to a mounting base 20 such as beds, platforms, working tables or the like by screwing bolts through the openings 13 of the track rail 2 and matching openings in the mounting base 20. The slider 1 has a casing 5 movable with respect to the track rail 2, and end caps 6 attached to the opposing ends of the casing 5. Provided on the upper surface of the casing 5 are openings 19 for fixture, by which other appliances, parts, chucks, grasping jaws or the like are mounted on the slider 1. Both the casing 5 and end caps 6 are formed on the lower surfaces thereof with recesses 10 by which the casing 5 and end caps 6 may saddle track rail 2 for free movement. The recesses 10 are each formed with raceway grooves 9 in opposition to the raceway grooves 4 on the track rail 2. The rolling elements 7, are confined for free movement in loaded raceways defined between the confronting raceway grooves 4 and 9. Retainer bands 18 are provided in the casing 5 so as to embrace the rollingelements 7 to thereby prevent the rolling elements 7 from falling out of the casing 5. Bottom seals 8 are secured to the lower surfaces of the slider 1 for closing clearances between the track rail 2 and slider 1.
The end caps 6 are provided therein with turnarounds for circulating the rolling elements 7. Mounted on the end caps 6 are end seals 17 for ensuring the sealing performance between the track rail 2 and the lengthwise opposing ends of slider 1. The end caps 6 and end seals 17 are secured to the opposing ends of the casing 5 by means of screws 16. The raceways defined by the confronting raceway grooves 4, 9, turnarounds formed in the end caps 6 and return passages 12 formed in parallel with the raceway grooves 9 in the casing 5, in combination, constitute endless-circulating paths for the rolling elements 7. Even though the rolling elements 7 are under loaded condition in the raceways, rolling-contact of the rolling elements 7 with the raceway grooves 4, 9 may help ensure the smooth movement of the slider 1 relative of the track rail 2.
To lubricate the relative sliding ways in the linear motion guide unit constructed as described above, grease or lubricating oil is usually employed. In case of grease, it is applied to the relative sliding ways through grease nipples 11. In contrast, lubricating oil is supplied to the sliding ways through pipe joints, which are used substituting for the grease nipples.
Japanese Patent Laid-Open No. 53637/1997 discloses a linear motion guide unit having for its object to provide a maintenance-free lubrication system. In the linear motion guide unit cited above, a reinforcing plate, lubricant-containing member and side seals, overlaid one on another in the order mentioned just above, are attached over each outer end surface of the end caps. The reinforcing plate is of steel plate that is formed into a substantially inverted U-shape, which is fit to the outward contour of the end cap and makes no contact with the track rail. The lubricant-containing member is also formed into a substantially inverted U-shape, which is fit to the contour of the end cap. The lubricant-containing member is provided on the inside thereof with convex portions, which are formed in adaptation with the cross section of the track rail so as to make the sliding contact with the upper and side surfaces of the track rail. For constant supply of the lubricant to the track rail, the convex portions of the lubricant-containing member are forced against the raceway grooves on the track rail by means of, for example, ring members inserted in holes formed in the lubricant-containing member, or by making the lubricant-containing member itself from elastic material. Pressing the lubricant-containing members against the raceway grooves on the track rail, however, renders the frictional force greater, resulting in causing the high frictional resistance adverse to the smooth movement of the slider.
Disclosed in Japanese Patent Laid-Open No. 200362/1996 is a linear motion guide unit having a sliding element that has fixed by clamping on end surfaces thereof with sealing means in which a lubricant-containing polymer member of the mixture of olefinic polymer with lubricant is adhered integrally to a polyolefin resin layer on a reinforcing plate. The lubricant-containing member is manufactured by the steps of melting the mixture of olefinic polymer with poly (.alpha.-olefin) oil or the like, pouring the mixture into a mould and solidifying the molded mixture by cooling under pressure. In the prior art described above, it is very hard to bond together the lubricant-containing polymer member with the reinforcing plate of core metal, because much oil in the lubricant-containing polymer member is present on the confronting surfaces to be bonded together. Moreover, olefinic polymer for the lubricant-containing polymer member is inherently unsusceptible to bonding with other materials. The lubricant-containing polymer member of olefin polymer should be integrated with the reinforcing plate made of only the same olefinic resins susceptible to olefinic polymer, or integrally fused with an olefinic polymer coating over the metal plate.
Japanese Patent Laid-Open No. 205534/1998 discloses a linear motion guide unit that comprises a sliding element movable on a track rail formed with raceway grooves, the sliding element being composed of a casing formed with raceway grooves, rolling elements running through between the confronting raceway grooves, end caps arranged on end surfaces of the casing, lubricating plates arranged on the end caps, and end seals secured on the lubricating plates. The lubricating plates are each composed of a sintered resinous member having porous structure immersed with lubricating oil. The lubricating plates are urged against the raceway grooves on the track rail by elastic actions of metallic frames covering around the peripheries of the lubricating plates.
If the lubricant in the lubricant-containing member might be applied to the raceway grooves on the track rail in the linear motion guide unit with no urging the lubricating plates against the raceway grooves by the action of the external force, the sliding resistance between the lubricant-containing members and the raceway grooves on the track rail may be reduced remarkably while the lubricant-containing members may be kept from wear owing to the sliding contact of the lubricant-containing members relatively of the track rail. However, even if the lubricant-containing members are free from such urging force towards the track rail, the lubricant-containing members of porous structure are insufficient in resistance against deformation. It is, therefore, desired to use a core plate high in stiffness to thereby prevent the lubricant-containing member from the deformation while supply the lubricant to the raceway grooves with sure reliability.